Field of the Invention
The invention relates to a device for fixing the position of a sheet on a feeding table of a sheet-fed printing press.
A printing press comprises a feeding table whereon a sheet is transported to a printing unit. During the transportation of the sheet, an edge of the sheet comes into contact with front lays which limit the movement of the sheet and define a line for aligning the sheet. After the alignment of the sheet, the front lay is moved away from the table, so that the edge of the sheet, which is disposed on the alignment or adjustment line, can be picked up by a gripper, and the sheet can consequently be transported to the printing unit.
From the published German Patent Document DE 40 04 447 C2, a feed lay or lay mark for aligning sheets which are guided on a feeding table have become known heretofore. The feeding table has an adjustable stop which is permanently connected to the feeding table. The feed lay is biased in the direction of the stop by a spring element. The front lay is articulatedly connected to a base body and can be pivoted together with the spring element from a working position into a neutral position. The working position is the position wherein the front lay defines the line for aligning the sheet. In the neutral position, the front lay is disposed beneath the feeding table, so that the front edge of the sheet can be picked up by a gripper.
A disadvantage of the arrangement described in the aforementioned German patent document is that the time at which the front lay leaves the stop is dependent upon the setting of the stop and is thus not precisely specified. This time uncertainty must be accounted for, and shortens the time available for aligning and stabilizing the sheet. The time at which the front lay leaves the working position must therefore be moved ahead or advanced accordingly. Wear is also to be expected due to the contact of the front lay with the adjustable stationary stop, which can result in the front lay being disadjusted or moved out of alignment.
The published German Patent Document DE 43 06 238 A1 discloses a device for fixing the position of a sheet, and a feed table for transporting the sheet, including a front lay that is disposed in the region of the feed table and that, in a working position, protrudes upwardly from the plane of the feed table, the front lay being fixed at a pivotable holding device and serving simultaneously as the adjusting device. Devices of this type are difficult to handle.
It is accordingly an object of the invention to make available an improved device for fixing the position of a sheet on a feeding table by aligning at front lays a sheet that is transported on a feeding table.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for fixing the position of a sheet, comprising a feeding table for transporting the sheet; at least one front lay disposed in vicinity of the feeding table and, in a working position, protruding upwardly beyond the plane of the feeding table; a swivellable holder to which the front lay and an adjusting mechanism for the front lay are secured; and an adjusting device secured to the holder, the front lay and the adjusting device being disposed separated from one another on the holder, the front lay being in continuous biasing engagement, under tension, with the adjusting device, so that, by changing the position of the holder, the front lay and the adjusting device are movable from the working position into a neutral position and, conversely, from the neutral position into the working position.
In accordance with another feature of the invention, the adjusting device is rotatably mounted, and is rotatable for adjusting the position of the front lay.
In accordance with a further feature of the invention, the adjusting device is formed with lock recesses and includes a lock element, the lock recesses cooperating with the lock element for enabling rotation of the adjusting device at prescribed angles.
In accordance with an added feature of the invention, the lock element is constructed as a leaf spring, which is prestressed with the aid of a lock nose in a direction towards the adjusting device and, when the adjusting device is rotated, the lock element catches in the lock recesses, so that the adjusting device is rotatable further only with increased torque.
In accordance with an additional feature of the invention, the position-fixing device includes a servomotor connected to the adjusting device for adjusting the rotational position of the adjusting device.
In accordance with yet another feature of the invention, the adjusting device is formed with a contact surface to which a tool for adjusting the position of the adjusting device is applicable.
In accordance with yet a further feature of the invention, the adjusting device is disposed beneath the feeding table; and the feeding table is formed with an opening in vicinity of the adjusting device, via which the contact surface is accessible with the aid of a tool.
In accordance with yet an added feature of the invention, the adjusting device includes a rotary element mounted so as to be rotatable about an axis of rotation; the front lay having a contact part in contact with a side margin of the rotary element; at least one of the rotary element and the position of the axis of rotation being constructed so that, when the rotary element is rotated about the axis of rotation, a spacing between the contact part and the axis of rotation is modified.
In accordance with yet an additional feature of the invention, the contact part and the rotary element are operatively connected to one another via at least one of an anti-friction bearing and a slide ring.
In accordance with still another feature of the invention, the adjusting mechanism serves for adjusting the spacing between the front lay and the adjusting device.
In accordance with still a further feature of the invention, the position-fixing device includes at least one tensioning device for prestressing the front lay in a direction towards the stop element.
In accordance with still an added feature of the invention, the front lay is formed at least partly of an elastic material; and is secured to the holding device in a manner that the front lay is prestressed in a direction towards the adjusting device.
In accordance with still an additional feature of the invention, the rotary element is formed as an Archimedes"" spiral.
In accordance with another feature of the invention, the rotary element is formed as a disk which is rotatable about an eccentrically disposed axis of rotation.
In accordance with a concomitant feature of the invention, the adjusting device is connected to a disk formed with lock recesses in a side margin thereof; the disk having a first and a second stop surface; and a stop bolt is disposed between the first and the second stop surfaces, the stop bolt, by coming into contact with the first and the second surfaces, serving to limit the range of rotation of the adjusting device.
The invention offers the advantage that the front lay is preferably prestressed against an adjusting device without play and connected to the adjusting device in one structural unit, the front lay being movable together with the adjusting device from a working position into a neutral position. In this way, the front lay is always in contact with the adjusting device, so that, subsequent to the transition from the neutral position into the working position, the front lay is aligned at the predetermined adjustment line.
Because at least two, and in most instances more than two, front lays are advantageously distributed over the width of the feeding table, it is expedient for the front lays to be individually adjustable. For straight sheet edges, all front lays can be used as stops for the sheet. The sheet edge is thus given optimal support in the stopping process.
For convex sheet edges, the middle front lays are preferably removed. Consequently, only two front lays at the outer region are used to prevent the sheet from rocking. For thin sheets with edges that are not straight, it may be necessary to adapt several front lays to the curvature of the sheet in order to prevent displacement or stressing of the sheet. This ensures an optimal adjustment of various printing materials.
A simple embodiment of the adjustable adjusting device calls for it to be rotatably mounted and provided with lock recesses. The rotatable mounting of the adjusting device ensures a simple adjustment of the position of the front lay. The use of lock recesses in conjunction with a lock element is advantageous in that the adjusting device is enabled to be rotated at prescribed angles in a precise manner. It is possible, thereby, to achieve very precise settings of the front lay.
In a preferred embodiment, the lock element is formed as a leaf spring having a lock nose which is allocated or assigned to the lock recesses. This embodiment ensures a cost-effective realization of the lock element.
The adjusting device is advantageously connected to a servomotor with which the position of the adjusting device can be set. The use of a servomotor permits a very precise adjustment of the adjusting device, which is additionally independent of the local position of the adjusting device. The adjusting device is thereby easy to adjust even when access thereto is difficult.
The adjusting device is also easy to adjust because it has a surface upon which a tool for adjusting the position of the adjusting device is able to be placed. Thus, the position of the adjusting device can be adjusted without using complex technical equipment.
The adjusting device is advantageously disposed beneath the feeding table, thereby providing a compact construction. In addition, an opening is formed in the feeding table in the vicinity of the adjusting device, via which the contact surface of the adjusting device can be accessed with a tool. In this way, the adjusting device can be adjusted easily from above.
The adjusting device is advantageously constructed in the form of a rotating element adjoined by the front lay via a contact part at a side margin of the rotating element. The rotating element and/or the axis of rotation of the rotating element are constructed so that, when the rotating element is rotated about the axis of rotation, the distance between the contact part and the axis of rotation is changed. This embodiment represents a simple construction of the adjusting device.
To prevent friction and to increase the accuracy of the position of the front lay, the contact part is braced against the adjusting device via a slide ring or anti-friction bearing.
In a further development of the invention, the front lay includes an adjusting mechanism with which the distance between the contact part and the front lay can be set. An initial setting of the front lay can be performed by using the adjusting mechanism. With this initial setting, a number of front lays can be aligned on a prescribed adjusting line.
In a preferred embodiment, the front lay is biased in a direction towards the stop element and the adjusting mechanism, respectively, by a tensioning mechanism. By using a prestressed front lay, freedom of play is afforded to the front lay in any situation.
A particularly advantageous embodiment of the invention provides for the front lay be produced at least partly from an elastic material. Additional stressing mechanisms for biasing the front lay in the direction towards the stop element are thus dispensed with or spared. A compact and economical construction is thereby possible.
A preferred embodiment of the rotating element is formed as an Archimedes"" spiral or a disk which is rotatable about an eccentrically arranged axis. In both embodiments, the distance between the side margin of the rotating element and the axis of rotation can be varied in dependence upon the rotational position of the rotating element.
Another advantageous embodiment of the invention is realized by an adjusting device comprising a disk at the outer margin of which lock recesses are provided, the disk being formed with first and second stop surfaces which are bringable into contact with a stop bolt. By using the stop bolt and the stop surfaces, a defined angular range is prescribed for the rotation of the adjusting device. A setting in which all the front lays stand on a common straight line is thereby easy to find.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for fixing the position of a sheet on a feeding table, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: